The present invention relates generally to signal detection, and more specifically to an improved application of the multiple signal classification (MUSIC) method by using a low order covariance matrix.
Electronic warfare (EW) receivers are required to receive simultaneous (time coincident) signals. If the signals are close in frequency and far apart in amplitude, they are difficult to distinguish as separate signals. For example, if the signals are sampled at 2.56 GHz, the input bandwidth is 1.28 GHz. If 256 samples are processed using a fast Fourier transform (FFT) method, the frequency resolution is 10 MHz. In this type of operation, it is difficult to detect signals with frequency separation of less than 10 MHz, which corresponds to the FFT frequency bin size in this example. In FFT-based EW receiver designs, the frequency resolution, that is, the capability to detect, or discriminate between, two signals, is usually larger than the FFT frequency resolution bin. However, operational requirements usually require a receiver to detect signals with closer frequency separations such as 1 MHz.
The multiple signal classification (MUSIC) method is a high spectral resolution method that might be used for digital receiver application, first described by R. O. Schmidt in 1979 in a limited distribution document, and later published in IEEE Transactions on Antennas and Propagation, “Multiple Emitter Location and Signal Parameter Estimation,” Vol. AP-34, No. 3, pp. 276-280 (March, 1986). Generally, the MUSIC method involves forming an autocorrelation matrix and finding its eigenvalue solution. To achieve a high spectral resolution using the traditional MUSIC method requires a large order number autocorrelation matrix. The computation solving the eigenvalue problem is very time consuming. Therefore, the hardware implementation becomes difficult, especially for receiver applications requiring real time multiple signal detection.
The MUSIC method is an example of a mathematical technique that once appeared to be only of academic interest, but, as the computational speed of computer hardware increases, may prove exceedingly valuable. Still, even with the improved computer hardware speeds just over the horizon, the computational requirements of the traditional MUSIC method are greater than will be able to be implemented for real time signal detection uses.
It is, therefore, an object of the invention to provide a modified MUSIC method that reduces the computational requirements while retaining the high spectral resolution advantages of the original method.